Diamond is a unique material that often exhibits extreme properties compared to other materials. Discovered about 30 years ago, the use of hydrogen in plasma-enhanced chemical vapor deposition (CVD) has enabled the growth and coating of diamond in film form on various substrate materials. CVD diamond research has been actively continued subsequently to develop new understanding and approaches for the growth and processing of this fascinating material. Currently, the study and development of diamond films has enabled a wide range of applications based on the combination of unique and extreme properties of diamond and the variety of film properties obtainable through tuning the microstructure, morphology, impurities, and surfaces. This issue of MRS Bulletin introduces the latest research, recent applications, and the challenges ahead for CVD diamond films.

Diamond has been attracting the attention of many researchers because of its potential for new applications such as in quantum devices and power electronics. These applications are enabled by the progress made in improving the quality of undoped, boron-doped, and phosphorus-doped diamond films grown by chemical vapor deposition techniques. Recent progress in diamond film growth and heterostructures of diamond and other compound semiconductors to realize these electronics applications are reported.

Diamond offers a unique combination of extreme physical properties. For many technological applications, diamond samples of the highest crystal quality are required to utilize the ultimate potential of the material. Specifically, grain boundaries, as in polycrystalline films, have to be avoided. In this article, the two major current approaches of synthesizing single crystal diamond by chemical vapor deposition are described. In homoepitaxy, high gas pressure and high power density microwave discharges facilitating growth rates above 50 µm/h form the basis for the deposition of mm-thick single crystal samples. Cloning and tiling followed by homoepitaxial overgrowth are promising novel concepts aimed at an increase in the lateral dimensions. Heteroepitaxial deposition on large-area single crystals of a foreign material represents a second alternative approach. The state of the art for both concepts is summarized, and current as well as potential future applications are discussed.

Diamond, because of its unique physical, chemical, and electrical properties and the feasibility of growing it in thin-film form, is an ideal choice as a material for the fabrication of reliable, long endurance, microelectromechanical/nanoelectromechanical systems (MEMS/NEMS). However, various practical challenges, including wafer-scale thickness uniformity, CMOS compatibility, surface micromachining, and, more importantly, controlling the internal stress of the diamond films, make this material more challenging for MEMS engineers. Recent advances in the growth of diamond films using chemical vapor deposition have changed this landscape since most technical hurdles have been overcome, enabling a new era of diamond-based MEMS and NEMS development. This article discusses a few examples of MEMS and NEMS devices that have been fabricated using mono-, nano-, and ultrananocrystalline diamond films as well as their performance.

Recent advances in biotechnology have fueled a need for well-defined, highly stable interfaces modified with a variety of biomolecules. Diamond is a particularly attractive material for biological applications because of its chemical stability and good biocompatibility. Since diamond can be made conductive by doping, it is also of interest for a variety of electrically based biological sensing applications that achieve improved performance through selective biological modification. Recent developments of diamond growth by chemical vapor deposition have enabled the preparation of large-area synthetic diamond films on different substrates at a reasonable cost. An as-grown diamond film is terminated by hydrogen on the surface and shows hydrophobic wetting characteristics, besides chemical inertness. This has created problems for attachment of many biomolecules that are inherently hydrophilic. The challenge to make diamond useful for in vivo applications thus lies in covalently linking biomolecules to such surfaces. Several breakthroughs have been accomplished over the last decade, and attaching biomolecules to diamond in a controlled and reproducible way can nowadays be achieved in several different manners and is the focus of this article.

Boron-doped diamond electrodes have attracted increasing interest from researchers due to their outstanding properties for electroanalysis and other electrochemical applications. Material quality and availability have come a long way since the initial reports on the basic electrochemical properties back in the late 1980s and early 1990s. In this review, we highlight how diamond electrochemistry has diversified and matured in recent years in terms of the understanding of structure-property relationships and the development of new applications of materials in electroanalytical chemistry.

Diamond films with good electron emission properties show great potential for applications such as electron sources. For single-crystalline diamond, the negative electron affinity at hydrogen-terminated surfaces enables efficient emission of conduction electrons into vacuum. Although electrons are not naturally present in the diamond conduction band, p–n junction diode structures make this possible; electrons are injected from n-type diamond to the conduction band of p-type diamond, giving rise to electron emission with efficiencies exceeding 1%. Alternatively, impacting electron beams can be used to inject “secondary” electrons into the conduction band, resulting in high emission gain. For ultrananocrystalline diamond (UNCD) films with versatile granular structure, enhanced electron field emission (EFE) properties can be achieved by altering the granular structure of the films. Utilization of nanoscale tips as templates for growing UNCD film or direct reactive ion etching of the film further enhances their EFE behavior. On the other hand, the release of electrons through application of thermal energy can be utilized in a thermionic energy converter to directly transform heat into electricity. With the addition of ion current from doped diamond emitters to the thermionic electron current, power output enhancement of the converter can be realized.

Hydrogen termination of diamond lowers its ionization energy, driving electron transfer from the valence band into an adsorbed water layer or to a strong molecular acceptor. This gives rise to p-type surface conductivity with holes confined to a subsurface layer of a few nanometers thickness. The transfer doping mechanism, the electronic behavior of the resulting hole accumulation layer, and the development of robust field-effect transistor (FET) devices using this platform are reviewed. An alternative method of modulating the hole carrier density has been developed based upon an electrolyte-gate architecture. The operation of the resulting “solution-gated” FET architecture in two contemporary applications will be described: the charge state control of nitrogen-vacancy centers in diamond and biosensing. Despite 25 years of work in this area, our knowledge of surface conductivity of diamond continues to develop.

New methods for the synthesis and deterministic assembly of advanced classes of nanomaterials enable integration of high-performence semiconductors with elastomeric substrates. These capabilities provide the foundations for a high-performance electronic and optoelectronic technology that can offer linear elastic mechanical responses to large strain deformations. The results create new opportunities in materials and device engineering, with important consequences in fields ranging from biomedicine to machine vision. This article summarizes the key materials science concepts and presents illustrative examples of their recent use in injectable, cellular-scale optoelectronic devices and in hemispherical compound eye cameras.